Voltage supply



'J. D. MCGHEE Dec. 8, 19.70

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VOLTAGE SUPPLY Dec. 8, 1970 3 Sheets-Sheet 2 Filed Feb. 9. 1968 J. D. MCGHEE VOLTAGE SUPPLY Dec. 8, 1970 f3 Sheets-Sheet 5 f, Z T N@ N .wmv Wmv W C g v o bw M 5v a W f y, .www ,5 Wmv .WNN humm WWW. SW H an A @m Ep EN M lo Almlm mmf Filed Feb. 9, Y 1968 .oonborboooboboob United States Patent O 3,546,626 VOLTAGE SUPPLY `lohn D. McGhee, Plymouth Meeting, Pa., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware Filed Feb. 9, 1968, Ser. No. 704,442 Int. Cl. HtlZm 3/28 U.S. Cl. 331-113 2. Claims ABSTRACT F THE DISCLOSURE An oscillator comprising a transformer having primary and secondary windings, each having input and output ends, the windings being poled in opposite directions; and a pair of push-pull transistors having input and output circuits, the output circuit of one of the push-pull transistors connected to the output end of the primary winding and the output circuit of the other connected to the secondary winding such that the push-pull transistors are alternatively driven conductive and non-conductive thereby developing an A.C. potential in the transformer. In a preferred embodiment the oscillator is employed to produce a D.C. voltage by rectifying and filtering the A.C. potential in the secondary winding.

CROSS REFERENCE TO RELATED APPLICATIONS This invention is particularly related to the subject matter of application Ser. No. 704,445, filed on the same day, entitled Energy Sensing Device by inventors Raymond W. Tabeling and John D. McGhee, in that the instant invention may be used in the system described and claimed therein to provide a stabilized D.C. voltage. This cross reference is merely illustrative and not intended to restrict the scope and/or use either invention.

In many electrical applications it is desirable to obtain a source of D.C. voltage that is stabilized against drift and line disturbances. For example, in the operation of a typical photomultiplier tube, a high negative stabilized D.C. voltage is required to bias the dynodes. Such a stabilized voltage may be supplied by the present invention. Also, by the practice of the instant invention, A.C. and various other D.C. signals may be produced.

In summary, the present invention relates to an oscillator comprising a transformer having primary and secondary windings each having input and output ends, said windings being poled in opposite directions; and a pair of push-pull transistors having input and output circuits, the output circuit of one of said push-pull transistors connected to said output end of said primary winding and the output circuits of the other connected to said secondary winding such that said push-pull transistors are alternatively driven conductive and nonconductive thereby developing an A.C. potential in said transformer.

For a better understanding of the invention, reference is made to the following description and the attendant drawings wherein:

FIG. 1 is a block diagram of a preferred embodiment of the invention;

FIG. 2 represents a detailed schematic of the embodiment of FIG. l;

FIG. 3 is a block diagram of another preferred embodiment of the invention; and

FIG. 4 depicts a detailed schematic of the embodiment of FIG. 3.

As readily apparent to one skilled in the art, oscillators, such as described hereinafter, may be run in the forward or reverse direction with the output adapted to provide stable or variable A.C. or D.C. signals. To best explain the nature of applicants invention, the following description will be directed, primarily, toward the adaptation of the invention to provide a stabilized, regulated D.C. potential to load.

In the embodiment illustrated in FIG. l, unregulated D.C. supply 1 provides an unregulated D.C. signal to the input of oscillator 2 which converts the D.C. signal to A.C. By subsequently rectifying and filtering the A.C. signal via rectifier 3 and filter 4, a D.C. signal is obtained at output terminal 5. To stabilize this signal, regulator 6 is incorporated in feedback relation between terminal 5 and D.C. supply 1. This regulator compensates for any increase or decrease of the signal from a preselected value the feedback signal to D.C. supply 1.

A detailed schematic of this embodiment is shown in FIG. 2. Referring to this figure, a 1Z0-v., 60-cycle line voltage is fed into primary winding 7. The transformer secondary winding 8 is center-tapped and connected in series with diodes 9 and 10, having common terminal 11. This arrangement is readily recognizable as a standard full-wave, center-tapped rectifier, the output of which iS a uctuating D.C. potential. This DLC. potential is subsequently smoothed by the filtering action of capacitor 12, coupled between conductor 13 and center-tap conductor 14, and capacitor 52, coupled between conductor 13 and ground. (Alternatively, this smoothed D.C. potential may be supplied by a battery or other suitable voltage source.)

The smoothed potential is then fed through conductor 13 to common-emitter connector 15 of oscillator 16. The voscillator includes a pair of transistors 17 and 18 connected in push-pull relation across the primary and secondary windings, 19 and 20, respectively, of transformer 21. The dot adjacent to one end of each winding indicates that the magnetic flux appearing in the core is of a determined direction whenever a current is applied to the dotted end of the winding. Whenever this current is increasing or decreasing in a winding, the dotted end of the winding is at a higher potential than the other end of that winding. The dotted end of each winding will be referred to hereinafter as the input end of the respective winding, with the other end being the output end. While transformer 21 can be almost any type of transformer, applicant has found that a television flyback transformer is particularly suitable. Also, though transistors 16 and 17 are shown to be NPN transistors, it should be apparent that PNP transistors could just as easily be used.

In this embodiment the input ends of primary winding 19 and secondary winding 20 are coupled together by means of conductor 22. This conductor is generally held at a fixed potential so that the oscillating voltage produced in secondary winding 20 is centered about a given potential. If, as in this embodiment, conductor 22 is grounded, a symmetrical A.C. potential is produced.

As shown, the collector of transistor 17 is connected to the output end of primary winding 19 by means of conductor 23, while the collector of transistor 18 is connected via conductor 24 to tap 25 of secondary winding 20'. To obtain a balanced output, tap 25 is preferably positioned such that length of secondary winding 20 from conductor 22 to tap 25 is equal to the total length of primary winding 19.

Feedbacks are provided from the collector of transistor 17 to the base of transistor 18 via capacitor 26 and resistor 27, and from the collector of transistor 18 to the base of transistor 17 via capacitor 28 and resistor 29.

Capacitors 26 and 28 are employed to block direct current feedback. Also connected to the bases of transistors 17 and 18 are resistors 30` and 31, respectively. These two resistors are coupled together to terminal 32,

which is, preferably, held at a fixed potential, e.g., ground.

The oscillator of this embodiment has been adapted to operate between the saturation states of push-pull transistors 17 and 18 as follows. Initially, the bases of both transistors are at ground. When the negative D.C. potential from the D.C. supply is applied to the emitters of both transistors, the voltage drop between the base and emitter of each transistor causes both transistors to start conducting. However, an electrical unbalance generally exists, even between transistors of the same type, so that one transistor initially conducts more heavily than the other. Such an unbalance is necessary in order to start the circuit into oscillation,

Assuming that transistor 18 initially pulls a greater current, the current flow in transformer 21 will be from the output end of primary winding 19 to tap 25 of secondary winding 20. This current flow turns ofi transistor 17 and capacitor 26 charges. The increase in current fiow in the indicated direction, caused by the initial conduction of transistor 18, is refiected from primary winding 19 into secondary winding 20. Thus, the current in secondary winding 20 includes both the original current fiowing through conductor 22 plus the induced current. This results in an increased current through conductor 22, with the cummulative effect being an overall increase in current through transformer 21 and transistor 18. As the current increases, the potential of the collector of transistor 18 decreases. Finally, transistor 18 reaches saturation and the potential of the collector equals that of the emitter. No further increase in current is possible. The induced voltage in secondary winding 20 drops to zero, resulting in a decrease in the total current flow. This decrease creates an induced voltage in the opposite direction, which further decreases the current fiow until current starts flowing in the opposite direction. Transistor 17 then turns on and transistor 18 turns off. As transistor 17 drives into saturation, capacitor 28 charges and capacitor 26 discharges. When transistor 17 reaches saturation, the current stops increasing and the cycle is repeated.

The output of oscillator 16 is an A.C. potential. The oscillator illustrated in this embodiment was adapted to produce an amplified signal by incorporating secondary winding having a larger number of turns than the primary winding.

The A.C. potential in secondary winding 20` is feed into a serially-connected, voltage-doubling rectifier that includes capacitor 33 and diodes 34 and 35. When the current flows from the input end to the output end of secondary winding 20, capacitor 33 charges via diode 34 and when flowing in the opposite direction, capacitor 33 discharges through diode 35. Diode 35 is connected in series to output terminal 36 through a filter comprising capacitors 37 and 38 and resistor 39. The grounded side of the filter is coupled to reference output terminal 40. The voltage appearing at terminal 36 is a high negative, D.C. potential.

Under ideal conditions, the output would be extremely stable. However, because of the presence of drift and line disturbances, it is desirable to employ a feedback to oscillator 16 to compensate for voltage variations at terminal 36. The feedback utilizes a typical series-regulator which comprises a control transistor 41 and an arnplifer. The amplier includes transistors 42, 43, 44 and 45 referenced by Zener diode 46.

The base of transistor 42 is connected via resistor 47 to the wiper of variable voltage-divider 48. Voltagedivider 48 is coupled to output terminal 36 through resistor 49 and to ground through variable resistor 50 and fixed resistor 51. If the voltage drop across Zener diode 46 is less than the voltage drop from ground to the wiper of voltage divider 48, transistor 42 conducts. The amount of current pulled through biasing resistor 53 by transistor 42 is dependent upon the voltage at output terminal 36 and the settings of voltage divider 48 and resistor 50, which provided coarse and fine adjustment, respectively.

The base and collector of transistor 42 are connected together by means of resistor 54 and capacitor 55 to reduce the high frequency A.C. gain of transistor 42. (This prevents the amplifier from going into oscillation.) The collector of transistor 42 is coupled through resistor 56 to the base of transistor 43 and through resistors 56 and 57 to conductor 13. The emitter of transistor 43 is biased by the voltage dividing action of resistors 58 and 59 which are connected to ground and conductor 13, respectively. The output of transistor 43 is fed into the base of transistor 44 via resistor 60 and to conductor 13 via resistors -60 and 61. Transistor 44 is coupled to conductor 13 through resistor 62 to transistor 45. A negative feedback, from the collector to the base o-f transistor 45 through capacitor 63 and resistor 64, is provided, as before, to prevent oscillations. The base is also connected to the emitters by means of resistor 65. The output of transistor 45 via resistor 66 controls the gain of control transistor 41 in parallel with resistor 67. Since the emitter of control transistor 41 is grounded, an increase or decrease in base current will provide a corresponding increase or decrease in the collector potential. This increase or decrease is filtered by capacitors 69 and 12 in combination with resistor 68, and transmitted to common-emitter connector 15 of oscillator 16 via conductor 14, secondary winding 8, diode 9 and conductor 13.

Voltage-divider 48 and resistor 50 are set so that the voltage supplied to load at output terminal 36 is at a predetermined value. If, because of a variation in A C. potential in primary winding 7 or for any other reason, the potential of output terminal 36 goes more negative than the predetermined value, the voltage of the base of transistor 42 drops. This drop causes transistor `42 to conduct more heavily, raising the potential of the base of transistor 43. When this happens transistor 43 and, necessarily, transistors 44 and 45 start to turn off. This reduces the current fiow in control transistor 41 which raises the potential of the collector of control transistor 41. This increase is fed, as previosuly described, to oscillator 16, reducing the negative potential of the emitters of pushpull transistors 17 and `18 and, consequently, the amplitude of the A.C. potential in secondary winding 20. This A.C. output is then rectified and lfiltered to provide a D.C. potential at output terminal 36 of the predetermined magnitude. Since there is a delay between the time the deviation in voltage is sensed and the time that it is returned to the predetermined value, a corrective phase lead is introduced by coupling the base of transistor 42 to conductor 13 through capacitor 69 and resistor 70. This lead dampens the response of control transistor 41, thereby preventing overcorrection. Otherwise, the voltage at output terminal 36 would oscillate each time a correction was made.

In FIG. 3, oscillator 71 is fed by unregulated D.C. supply 72. The D.C. output of oscillator 71 is rectified and filtered to D.C. by rectifier 73 and filter 74. The D.C. signal at output terminal 75 is regulated and stabilized by feedback through regulator 76 which applies a corrective signal directly to oscillator 71, thereby maintaining the output signal at the desired level.

A detailed schematic of this embodiment is shown in FIG. 4 wherein the unregulated D.C. supply includes a full-wave, center-tapped rectifier and a filter. The rectifier is substantially the same as that described in the previous embodiment, with the A.C. line input supplied to primary winding 77, reflected in secondary winding 78 and rectified by employing diodes 79 and 80 and center tap 81. One difference is that center tap 81 is grounded. Since the D.C. supply is not regulated by feedback, it is desirable to minimize output variations by tying the center of secondary winding 78 to a fixed potential. The output of the rectifier is smoothed by the filter formed by capacitors 82 and 83, connected to ground and opposite ends of resistor 84. (Again, a battery or other D.C.

source may be used to provide an unregulated D.C. signal.)

The filtered signal is introduced into common-emitter connector 85 of oscillator 86 via conductor 87. The oscillator incorporates push-pull transistors 88 and 89 coupled across opposite windings of transformer 90. In this embodiment the regulation of oscillator 86 is provided by varying the bias signal applied to the bases of transistors 88 and 89 through conductor 91 and serially-connected resistors 92 and 93. The collectors of transistors 88 and 89 are connected to tap 94 of secondary winding 95 and to the output end of primary winding 96, respectively. The windings of transformer 90 are poled in opposite directions and connected, preferably, by xed-potential conductor 97. The earlier designations of input and output ends are retained. A.C. feedbacks from the collector of transistor 88 through capacitor 98 and resistor 99 to the base of transistor 89 and from the collector of transistor 89 through capacitor 100 and resistor 101 to the base of transistor 88 are provided.

The operation of oscillator 86 is the same as that of oscillator 16 of FIG. 2, except that push-pull transistors 88 and 89 operate between unsaturated conduction states as determined by the base bias potential.

The A.C. output from oscillator 86 through secondary winding 95 is rectified by a serially-coupled rectifier. The rectifier is a voltage doubler that draws electrons through diode 102 into capacitor 103 on one-half of the cycle and discharges them via diode 104 on the other half. The resulting negative D.C. potential is smoothed by a filter, consisting of resistor 106 and capacitors 107 and 108, connected between diode 104 and output terminal 105.

The negative potential at output terminal 105 is controlled by a regulator that is coupled between output terminal 105 and the bases of push-pull transistors 88 and 89 of oscillator 86. The regulator includes voltage divider 109, an amplifier referenced by Zener diode 110 and a control transistor 111. Voltage divider 109 is connected to output terminal 105 through resistor 112 and to ground through variable resistor 113 and fixed resistor 114. The potential of the wiper of voltage divider 109 is set by coarse adjustment of the divider itself and by fine adjustment of resistor 113. This potential determines the feedback through transistors 115 and 116 of the ampliiier to the base of control transistor 111. Transistor 115 is connected through its base to the wiper of voltage divider 109, through its emitter to Zener diode 110, and through its collector to the base of transistor 116. The collector of transistor 115 is tied to ground by resistor 117. The base of transistor 115 is connected through capacitor 118 to resistor 119 thereby providing a phase lead to dampen the input to the base, as the oscillator voltage builds up.

Zener diode 110 is held at its breakdown voltage to provide a xed reference level by connecting it to a filter, consisting of resistor 119 and capacitor 120, which is coupled to rectifying diode 121, which, in turn, is connected to the collector of transistor 88. Diode 121, however, does not conduct until oscillator 86 starts to operate. Therefore, it is necessary to provide alternative current path from the emitter of transistor 115 so that transistor 115 initially conducts. Otherwise, no bias signal would be supplied to the bases of push-pull transistors 88 and 90. The alternative current path, sometimes called a guaranteed turn-on, is provided by connecting diode 122 between the emitter of transistor 115 and a voltage divider formed by resistors 123 and 124. The upper end of resistor 123 is grounded while the lower end of resistor 124 is coupled to the regulated D.C. supply via conductor 125, common-emitter connector 85 and conductor 87. The output of transistor 115 is fed to transistor 116 which is connected to common-emitter connector 85 by conductor 125 and to the base of control transistor 111 through resistor 126. The output from transistor 116 determines the voltage drop across control transistor 111 which, in turn, varies the feedback to the bases of pushpull transistors -88 and 89.

The operation of the regulator is as follows. First, assume that the D.C. potential across output terminal and grounded reference terminal 127 becomes less negative than a preset value as determined by voltage divider 109 and resistor 113. This raises the potential of the base of transistor 115, causing transistor 115 to pull more current. This causes transistor 116 to conduct more, heavily, which increases the base current of control transistor 111. As the base current is reduced, transistor .111 pulls less current and its collector goes more positive, driving the bases of push-pull transistors 88 and 89 more positive. This increases the amplitude of the output of oscillator 86 thereby restoring the D.C. potential to the original preset value. Since there is a delay between the time the signal is fed back through the wiper of voltage divider 109 and the time that the D.C. potential at output terminal 105 is restored to the preset value, capacitor 128 is connected between the wiper of voltage divider 109 and ground to prevent overcorrection.

While the present invention has been primarily described in conjunction with the production of a regulated, stabilized D.C. signal, the present invention can be adapted to produce regulated or unregulated, stabilized or unstabilized, A.C. or D.C. signals. For example, the embodiment of FIG. 1 can function as a regulated, stabilized A.C. supply by providing a load output between oscillator 2 and rectifier 3.

It will be understood that various changes in the details, materials, steps, and arrangement of parts, which have been herein described and illustrated, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims.

What is claimed is:

1. In a D.C. voltage supply comprising:

a transistorized oscillator including a transformer comprising primary and secondary windings, each having input and output ends, said windings being poled in opposite directions, and a pair of push-pull transistors having input and output circuits, the output circuit of one of said push-pull transistors connected to said output end of said primary winding and the output circuit of the other transistor connected to said secondary winding such that said push-pull transistors are alternatively driven conductive and nonconductive, thereby developing an A.C. potential in said transformer;

a voltage means for supplying a D.C. voltage to the input circuit of said push-pull transistors;

a rectifying means connected to said output end of said secondary winding to convert said A.C. potential to a D.C. potential;

a filtering means coupled to said rectifying means to smooth said D.C. potential;

an output terminal connected to said filtering means;

and

a regulating means electrically positioned between said output terminal and said oscillator for providing a D.C. feedback to said oscillator to control the magnitude of said D.C. potential;

the improvement wherein said regulating means comprises a variable voltage dividing means, an amplifying means, a control transistor having a base, collector, and emitter, and a Zener diode, said variable voltage dividing being coupled between said output terminal and said amplifying means for varying the input to said amplifying means, thereby allowing adjustment of said D.C. potential at said output terminal, said amplifying means being additionally connected to the emitter of said Zener diode and to said base of said control transistor, said collector of said control transistor being resistively connected to said supply means and said emitter of said control transistor being connected to said lixed potential conductor of said oscillator thereby supplying said source of positive D.C. potential thereto, said emitter of said Zener diode being additionally connected resistively to said source of negative D.C. potential, and the collector of said Zener diode being connected to said xed potential conductor, said amplifying means and said Zener diode providing a D C. potential to said` base of said control transistor such that the collector-emitter resistance of said control transistor is varied as a function of said D.C. potential at said output terminal whereby said D.C. potential at said output terminal is maintained at a preset value.

2. In an A.C. voltage supply comprising:

a transistorized oscillator including a transformer comprising primary and secondary windings, each having point and output ends, said windings being poled in opposite directions, and a pair of push-pull transistors having input and output circuits, the output circuit of one of said push-pull transistors connected to said output end of said primary winding and the output circuit of the other connected to said secondary winding such that said push-pull transistors are alternatively driven conductive and nonductive, thereby developing an A.C. potential in said transformer;

a voltage means for supplying a D.C. voltage to the input ciriuit of said push-pull transistors;

an output terminal connected to said output end of said secondary winding;

a rectifying means connected to said output terminal to convert said A.C. potential to a D C. potential;

a ltering means coupled to said rectifying means to smooth said D.C. potential; and

a regulating means electrically positioned between said -tltering and said oscillator for providing a D.C. feedback to said oscillator to control said A.C. potential at said output terminal;

the improvement wherein said regulating means vcomprises a variable voltage dividing means, an amplifying means, a control transistor having a base, collector, and emitter, and a Zener diode, said variable voltage dividing being coupled between said output terminal and said amplifying means for varying the input to said amplifying means, thereby allowing adjustment of said A.C. potential at said output terminal, said amplifying means being additionally connected to the emitter of said Zener diode and to said base of said control transistor, said collector of said control transistor being resistively connected to said supply means and said emitter of said control transistor being connected to said xed potential conductor of said oscillator thereby supplying said source of positive D C. potential thereto, said emitter of said Zener diode being additionally connected resistively to said source of negative D C. potential, and the collector of said Zener diode being connected to said Xed potential conductor, said amplifying means and said Zener diode providing a D.C. potential to said base of said control transistor such that the collector-emitter resistance of said control transistor is varied as a function of said A.C. potential at said output terminal whereby said A.C. potential at said output terminal is maintained at a preset value.

References Cited UNITED STATES PATENTS 2,987,664 6/1961 Poirier et al. 331-113 3,200,348 8/1965 Kammiller et al. 331-113 3,305,756 2/1967 Doss et al. 331-113 3,327,199 6/1967 Gardner et al. 331-113 3,387,228 6/1968 Randall 331-113 2,982,881 5/l- 96\l Reich 331-112 3,066,265 11/1962 Janssen et al. 331-112 3,132,309 5/1964 Constable 321-2 3,161,785 12/.1964 Carin 331-113 3,274,478 9/ 1966 Hollmann et al. 321-2 3,300,705 1/1967 Hunstad 331-112 3,412,311 11/1968 Siedband 331-113 OTHER REFERENCES Popular Electronics, Up-Verter, Ben Richards,

October 1967, pp. 67-69.

JOHN KOMINSKI, Primary Examiner U.S. Cl. XJR. 

